Solar pyrolysis of waste rubber tires using photoactive catalysts

The solar pyrolysis of waste tire rubber was investigated with the application of heterogeneous photocatalysts including TiO₂, Pd/TiO₂, Pt/TiO₂, Pd-Pt/TiO₂, and Bi₂O₃/SiO₂/TiO₂. Experiments were performed at temperatures ranging between 550 and 570 °C under solar irradiations of 950-1050 W/m². The gas yield from non-catalytic solar pyrolysis was at 20% while the use of TiO₂ catalyst increased the gas yield to 27%. Doping of TiO₂ with noble metals and Bi₂O₃/SiO₂ metal oxides enhanced further the cracking ability of the catalyst. Bi₂O₃/SiO₂/TiO₂ gave a 32% gas yield. The highest gas yields of 40% and 41% were achieved over Pd-Pt/TiO₂ and Pd/TiO₂ catalysts, respectively. Catalyst characterization by BET, SEM, EDX and XRD showed the role of metal doping in altering the morphology of TiO₂, resulting in nanocrystallites, larger pore volume and higher surface area. Both, Pd and Bi influenced the photocatalytic properties of TiO₂ improving cracking activity during pyrolysis of waste rubber.